The Evolutionary Psychology FAQ

Edward H. Hagen, Institute for Theoretical Biology, Berlin

How can we identify psychological adaptations?

We can identify psychological adaptations using the same criteria we use to identify any other adaptation: EVIDENCE OF DESIGN. We know the lung is an adaptation because 1) the many features of the lung--numerous chambers of gas-permeable tissue each surrounded by a network of blood vessels and each connected to the windpipe--correspond precisely to the nature of the problem: transferring oxygen to the blood, 2) solving this problem (oxygenating blood) would have greatly facilitated reproduction in ancestral environments (as it does in modern environments), and 3) natural selection is the only source of functional organization. QED, the lung is, without doubt, an adaptation. We can use these same criteria to identify psychological adaptations.

In order to effectively solve reproductive problems, mechanisms (a.k.a. adaptations, functions, modules, organs) must possess a suite of specific structural features that effect the required transformations of the world. These features are called 'design features.' The gas-permeable chambers, surrounding blood vessels, and connections to the windpipe constitute some of the design features of the lung. By precisely specifying the nature of a particular reproductive problem (a process sometimes referred to as a task analysis), we can, a priori, describe the design features that a putative adaptation must possess if it is to effectively solve the problem. This is as true of information processing problems as it is of any other type of reproductive problem. For the case of psychological adaptations, we must first identify an information processing problem faced by humans in the EEA. We must then determine the features that any psychological adaptation designed to solve this problem must possess. Finally, we seek both direct and indirect evidence that the nervous system possesses the required design features--that is, that it can solve the reproductive problem. The more design features that are necessary to solve the problem, and the more such features that the nervous system appears to possess, the higher the probability that a psychological adaptation to solve the reproductive problem in fact exists. Thus, the determination that a psychological adaptation exists is an inherently probabilistic enterprise.

A hypothetical example: suppose we can make the case that navigating in unfamiliar terrain would have been a reproductively important ability for ancestral humans. We would then specify all the information processing features relevant to solving this problem: measuring the angle of the sun, keeping accurate track of time, integrating velocity vectors, etc. We could then conduct numerous experiments to determine whether humans in fact possess each of these abilities, and, if so, whether they are properly integrated so that humans can effectively navigate in unfamiliar terrain. The more such abilities we can identify in humans, the greater the probability that humans possess a psychological adaptation for navigating in unfamiliar terrain.

Copyright 1999-2002 Edward H. Hagen